Diurnal Cycle of the Atmospheric Mixed Layer during DYNAMO/CINDY/AMIE

The DYNAMO/CINDY/AMIE field campaign, conducted over the Indian Ocean from October 2011 to March 2012, was designed to study the initiation of the Madden-Julian Oscillation (MJO). Two prominent MJOs occurred in the experimental domain during the Special Observing Period in October and November. Data from atmospheric soundings at Gan Island and the R/V Revelle, as well as the S-Pol radar on Gan Island, are used to study the temporal variation of the atmospheric mixed layer during the experiment. For the soundings, both the potential temperature and specific humidity profiles are used to determine the mixed layer depths at 3-hourly intervals. For the radar, the mixed layer depth was determined based on Bragg scattering analysis.

Results indicate that the atmospheric mixed layer varies on multiple time scales throughout the campaign, ranging all the way from the monthly MJO time scale to short time scales associated with the diurnal cycle and individual convective systems. The mixed layer at the Revelle determined by the soundings exhibits a clear signal associated with the passage of both the October and November MJOs, while the amplitude of the MJO signal at Gan Island is somewhat less. Both sounding and S-Pol data at Gan Island reveal a diurnal-cycle range of the mixed layer depth of ~100 m on undisturbed days, but less of a variation during the convectively disturbed, active phase of the MJO. Analysis of the diurnal cycle at the Revelle is underway and will be reported on at the conference.